An unexpected behavior lookup: ```python >>> ast.FormattedValue(ast.Str('ss')).conversion >>> ast.unparse(ast.FormattedValue(ast.Str('ss'))) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/lib/python3.9/ast.py", line 1564, in unparse return unparser.visit(ast_obj) File "/usr/local/lib/python3.9/ast.py", line 801, in visit self.traverse(node) File "/usr/local/lib/python3.9/ast.py", line 795, in traverse super().visit(node) File "/usr/local/lib/python3.9/ast.py", line 407, in visit return visitor(node) File "/usr/local/lib/python3.9/ast.py", line 1153, in visit_FormattedValue self._fstring_FormattedValue(node, self.buffer_writer) File "/usr/local/lib/python3.9/ast.py", line 1178, in _fstring_FormattedValue conversion = chr(node.conversion) TypeError: an integer is required (got type NoneType) >>> ast.unparse(ast.FormattedValue(ast.Str('ss'), -1)) 'f"{\'ss\'}"' ``` ast.FormattedValue conversion's default value is expected to be -1 but not None See: https://docs.python.org/3/library/ast.html#ast.FormattedValue Other: If certainly, it's also a bug on typeshed.